1. Field of the Invention
The present invention relates to screw drivers, and more particularly to screw drivers that have a spindle idling speed of about 5000 to 7000 rpm, when not fastening screws.
2. Description of the Related Art
Power screw drivers may be utilized to fasten screws to a variety of objects, such as decorative boards, plasterboards, asbestos boards or similar boards (hereinafter simply referred as xe2x80x9cboardsxe2x80x9d) for the interior of an architectural structure by utilizing self tapping screws, such as wood screws, drywall screws and texscrews (hereinafter simply referred as xe2x80x9cscrewsxe2x80x9d). As shown in FIG. 9 to FIG. 13, a user M may utilize a screw driver T to fasten a screw into a board using a variety of postures. For example, user M may fasten the screw into a floor board while standing in a downward posture as shown in FIG. 9 or in an upward posture as shown in FIG. 12. Moreover, user M may fasten the screw into a wall board by holding the screw driver T at the level of the user""s waist as shown in FIG. 10, or at the level of the user""s shoulders as shown in FIG. 11 or at the level of the user""s head as shown in FIG. 13. In FIG. 9 to FIG. 13, symbol M represents the user of the screw driver, symbol T represents the screw driver, symbol F represents the floor, symbol K represents the wall and symbol J represents a ceiling.
A pushing force is necessary to push the screw driver in a screw-fastening direction in order to perform the screw-fastening operation. The user""s ability to provide a strong pushing force is generally diminished when the user holds the screw driver at the level of the user""s head as shown in FIG. 13. A similar problem occurs when the user fastens the screw in an upward posture as shown in FIG. 12. As the pushing force for fastening the screw is reduced, the burden on the user to utilize the screw driver will increase, because the screw-fastening performance depends not only on the rotation speed of the spindle of the screw driver, but also on the pushing force applied by the screw driver. Thus, if the spindle rotation speed is a constant, the screw-fastening performance will vary only based on the pushing force. In known screw drivers, the standard spindle revolution speed is within a range of 1800 rpm to 2500 rpm. With known screw drivers, when the pushing force is reduced, the screw-fastening performance is significantly affected and the user of the screw driver tends to become tired.
It is, therefore, an object of the present invention to provide improved screw drivers that reduce the burden on the user.
Preferred screw drivers may include a motor coupled to a spindle for driving a bit. The bit can be inserted into the head of the screw in order to drive the screw into an object, such as a board. The screw driver may preferably fasten a screw that has a pitch within a range of 1.3 mm to 2.0 mm, as well as a range of {fraction (1/32)} inch to {fraction (3/32)} inch. Most preferably, the spindle may idle at a speed within a range of about 5000 rpm (revolutions per minute) to about 7000 rpm in order to increase the screw driving performance when the user begins to drive a screw into an object.
Because the spindle rotates at a relatively high revolution speed, the screw-fastening operation can be completed more quickly, even if the user is fatigued. Thus, preferred screw drivers assist the user in easily performing screw-fastening operations.
Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.